There are known the following so-called single-site catalysts, which polymerize an addition-polymerizable monomer such as an olefin to produce an addition polymer:
(1) a catalyst obtained by combining bis(cyclopentadienyl)zirconium dichloride with methylaluminoxane, and a catalyst obtained by combining said transition metal compound with a specific boron compound (JP 58-19309A, corresponding to U.S. Pat. No. 4,542,199);
(2) a catalyst obtained by combining bis(cyclopentadienyl)zirconium dimethyl with tri(n-butyl)ammonium tetraxis(pentafluorophenyl)borate (JP 1-502036W, corresponding to EP 277004A); and
(3) a catalyst, which slightly lowers homogeneity of an addition polymer obtained (JP 5-320248A, corresponding to EP 571987A, JP 10-17617A, JP 11-12319A and JP 11-343306A), wherein the term “homogeneity” means uniformity of polymerization of a comonomer in case that said addition polymer is a copolymer.